Control system



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Jan. 23, 1962 P. PRoFos 3,017,869

CONTROL SYSTEM Filed Feb. 14. 1957 4 Sheets-Sheet 3 E M PER/1 TUIFECONTROLLED DEV/CE 46 A TT'ORNE) P. PROFOS CONTROL SYSTEM Jan. 23, 1962 4Sheets-$heet 4 Filed Feb. 14, 1957 32 INVENTOR. PA UL PROFOS.

Illliillll Illl o BY K/f A TTORNEK United States 3,017,869 CONTROLSYSTEM Paul Profos, Winterthur, Switzerland, assignor to Sulzer Freres,S.A., Winterthur, Switzerland, a corporation of Switzerland Filed Feb.14, 1957, Ser. o. 640,196 Claims priority, application Switzerland Feb.15, 1956 7 Claims. (or. 122-479 The present invention relates to amethod and means for changing the values or reference inputs to bemaintained by regulators of an energy producer, more particularly of asteam generating apparatus, so that different values are maintained bythe regulators at different outputs, the change of the adjustment of thevalue to be maintained by the regulators being effected a period of timeafter the regulators have responded to a new load condition.

When operating a producer of energy, for example, a forced flow steamgenerator there is, when the load is constant, a thermodynamicequilibrium between the supply of operating media, namely fuel,combustion air, water, and the characteristics of the output, namelyamount, pressure, and temperature of the produced steam. Thisequilibrium is disturbed when the load is changed and is not restoreduntil all operating factors are balanced relatively to one another andare in agreement with the new load and the control oscillations of theindividual regulators have subsided.

There are several possibilities of adjustment of the regulators tocomply with the new load. It may be desirable to change the pressure ofthe live steam according to the load, particularly in forced flow steamgenerators operating at very high pressures and at great loadvariations. If the steam pressure is so changed that the inlet flow areaof a turbine receiving steam from the steam generator is the same at allloads, the control method is known as the sliding pressure method. Theadvantage of this method resides in the fact that the turbine isoperated at optimum efficiency at all loads. This method ensures bestoverall operating efficiency of the plant, particularly at frequentpartial load conditions.

The sliding pressure method, however, is objectionable because theoperating conditions of the steam generator must be built up until thenew load is obtained. There is a time lag or delay between the changeseffected at the inlet of the tube system of a forced flow steamgenerator and the changes produced thereby at the outlet of thetube'system. These changes are amplified by the natural inertia of anysteam generator due to its accumulating capacity. Therefore, quickchanges of load cannot be effected by the sliding pressure method. Ifquick changes of load are forced on the steam generator with a deviationfrom the sliding pressure operation, considerable operating difficultiesare encountered, particularly because of disturbances of the temperatureregulation and maintenance of the steam pressure.

Because of the shortcomings of the true sliding pressure method, theso-called step pressure method has been suggested in which loadvariations are met at first by maintenance of the steam pressure and bysubsequently gradually and manually adjusting the live steam pressure tothe new load. This method is desirable from the standpoint of the steamgenerator operation but has the disadvantage that the turbine operates aconsiderable length of time below optimum efficiency so that the overallefficiency of the plant is at least temporarily reduced. The method is,therefore, applicable only to plants in which load variations occurrelatively seldom.

It is; desired to automatically change the individual operatingcharacteristics; of an energy producer, for

Bfil'ififi Patented Jan. 23, 1962 example, a steam generator, i.e., toadjust the steam pressure, the steam temperature, the temperature of thefeed water, the supply of feed water, of fuel, of air, etc., inaccordance with the load and to a predetermined degree so that thesecharacteristics are different at different loads. The manner in whichthese changes are produced is of utmost importance.

If the value to be maintained by a regulator is too quickly changed tomeet the new load the control operation taking place during the changeof load is disturbed, causing prolonged and increased controloscillations until equilibrium is obtained after the change of load,

If the value to be maintained by a regulator is changed too slowly at achange of load, energy losses are produced because the energy produceroperates too long at unfavorable efilciency conditions.

It is known to delay control effects in steam power plants byinterposing an integrating system in the control mechanism. Such asystem, which may be called a transmission system of the first order,consists of a resistance and of an accumulating element, for example, athrottling device through which a regulating medium flows into anaccumulator, or an electric resistance through which an electriccondenser is charged.

If an energy carrier is supplied through a throttle device to anaccumulator, the energy condition of the latter is changed, the changebeing produced the quicker, the smaller the throttle effect and thesmaller the capacity of the accumulator. This arrangement is notsuitable for solving the problem of changing the value to be maintainedby a regulator, because at momentary load changes, the change of thevalue to be maintained by the regulator is initiated instantaneouslyaccording to a linear time function. The control operation of a controlcircuit, for example, of a temperature regulation, receives not only acontrol pulse caused by the change of the load, but also a disturbingpulse because of the quick change of the adjustment of the value to bemaintained by a regulator at the critical moment of the controloperation. Experience has shown that the control operation with aninstantaneous change of the value to be maintained by the regulator isworse than a control operation with no change of the reference input ofthe regulator.

It is an object of the present invention to provide a method and meansfor controlling the retarding characteristic of the adjustment of thevalue to be maintained by a regulator so that the resetting of theapparatus for adjusing the value to be maintained by the regulator iscompleted not sooner than the regulating oscillations have abated in thecontrol circuit of the regulator and so that a graph showing theadjustment as a function of time begins with a horizontal tangent andthereupon gradually approaches the new value to be maintained by theregulator. With this method the control operation of the control circuitis not adversely affected by the resetting of the reference input of theregulator.

It is desirable that the adjustment of the value to be maintained by theregulator is effected in such manner that the new value is approachedasymptotically. Ac.- cording to the invention the adjustment of thevalueto be maintained by the regulator is so performed that there is atfirst an idle period after which the new value is gradually attained. Itis important that the idle period T amounts to at least 5% of thestarting period T,, of the adjustment. Because of the different lengthsof time elapsing between the initiation and the effect of a controlpulse for different regulating circuits, as, for example, for combustionmaterials, feed water supply, waterinjectio n, and the like, it isnecessary that different lengths of time are provided for the change ofthe value to be. maintained by regulators for different operating media.These lengths of time must be so that the adjustment of the new valuemaintained by each regulator is completed not sooner than the regulatingoscillations caused by a change of load in the respective regulatingcircuit have subsided.

The oscillation period of a control circuit after reeeiving a controlpulse of a certain magnitude can be calculated or found by tests on theenergy producer. The oscillating period of a control circuit is the timewithin which the oscillating amplitude caused by a control or adisturbing pulse abates below a predetermined permissible minimum value.After determination of the oscillating period of a control circuit thetime is determined which is needed for resetting the apparatus foradjusting the value to be maintained by the respective regulator toconform with the new load.

The method of adjusting the value to be maintained by a regulatoraccording to the invention can be performed by hand; it is, however,preferred to use an automatic control apparatus. Such an apparatusincludes a load measuring device interposed in the conduit connectingthe energy producer with an energy consumer and responding to the loadon the energy producer, the load measuring device being connected withdevices for adjusting the values to be maintained by individualregulators which are needed for controlling the energy producer. Theapparatus according to the invention includes a modifying or retardingdevice interposed between the load measuring device and the device foradjusting the value to be maintained by a regulator, the retardingdevice including at least two pulse delaying or damping and accumulatingunits arranged in series relation, each of the units including aresistance element and an accumulating "element for the control pulseenergy emitted by the load measuring device.

The novel features which are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, and additional objects and advantages thereof will bestbe understood from the following description of embodiments thereof whenread in connection with the accompanying drawing in which:

FIG. 1 is a diagrammatic illustration of a steam power plant equippedwith control apparatus according to the invention;

FIG. 2 is a diagrammatic illustration of a sender or retarding deviceaccording to the invention;

FIGS. 3a to 3d are diagrams relating to the operation of the controlsystem according to the invention;

FIG. 4 is a more detailed diagrammatic illustration of a steam powerplant equipped with control apparatus according to the invention;

FIG. 5 is a diagrammatic illustration of a control system according tothe invention.

Like parts are designated by like numerals in several figures of thedrawing.

Referring more particularly to FIG. 2 of the drawing, numeral 28designates a rod connected with and receiving pulses from a conventionalload measuring device. The rod 28 is connected with a first accumulatingelement 29 which is in the form of a coil spring. The far end of thecoil spring is connected by means of a rod 28 with a dash pot orthrottling element 30. The piston of the latter is connected by a rod28" with a second accumulating element 31, which is also in the form ofa coil spring whose far end is connected with a second dash pot orthrottling element 32. The piston of the dash pot 32 is connected with alever 34 which transmits the accumulated pulse to the adjustingapparatus for setting the value to be maintained by a regulator. Thedash pots 30 and 32 include conventional throttle valves 33 and 33',respectively, by means of which the time values T, and T, can beincreased or decreased, as desired, for tuning the transmission deviceshown in FIG. 2 to the duration of the control oscillations of itsrespective control circuit.

According to the invention an individual retarding unit or sender may beprovided for each adjusting device for setting the value to bemaintained by the regulator. This, however, would require complicatedmechanisms.

It is usually suflicient to provide only two retarding units or senderswhich are directly or indirectly connected with groups of devices foradjusting the settings of several regulators, one group consisting ofregulators in which the adjustment must be performed very slowly and theother group including the regulators in which the adjustment can beperformed relatively quickly.

FIG. 30 is a diagram in which the movement produced by the lever 34 isplotted relatively to the time. The dash-dot curve K represents thefunction of the adjustment of the value to be maintained by a regulatorin dependence on the time.

Letter W designates a line which is tangent to the point of inflectionof the dash-dot curve K The intersections of the line W with thehorizontal lines S and S which show the positions of the device foradjusting the values to be maintained by a regulator before and after achange of load, determine the time period T, during which the adjustingdevice is inactive and the time period T during which the adjustment isstarted.

FIG. 3d shows the adjustment function curve obtained with a transmissionor retarding device of the first order, i.e., with a single integratingelement. This curve begins with a steep, substantially vertical tangentand gradually approaches the new value to be maintained by the regulatorwhereby the speed of adjustment diminishes. With a retarding device ofthis type the value maintained by the regulator is changed very quicklyat the moment of a change of the load, the speed of change diminishingthereafter, i.e., the change is effected at greatest speed at thebeginning of the control operation, at a time when the disturbances ofthe equilibrium of the system caused by the control pulse are greatest.For this reason a single integrating element is unsuitable for thesolution of the problem which is the object of the present invention.

FIGS. 3a, 3b, and 30 show diagrams illustrating the adjustment of thevalue to be maintained by a regulator according to the invention,employing a transmission device of the second order. These figures showthe time T as abscissae. FIG. 3a shows the load M of the energy produceras ordinates. The ordinates in FIG. 3b designate the item F to becontrolled, for example, fuel supply, air supply, water supply,pressure, temperature, water injection, and the like. The ordinates S inFIG. 3c indicate the positions of the device for adjusting the values tobe maintained by a regulator.

In case of a sudden load change the load M in FIG. 3a is instantaneouslychanged to the load M The disturbing pulse produced by the change of theload causes a change of the value F. Because of the inertia of thesystem the change of the value F begins very slowly and increases at agradually increasing rate. Thereupon the control mechanism reverses theregulating effect so that the value F is changed to a new value F withina certain period of time in gradually diminishing waves.

In the meantime the load measuring device has emitted a pulse AScorresponding to the new value to be main tained by the regulator to thesender for readjusting the setting device of the regulator. The senderretards the transmission of the pulse. The curve K in FIG. 3c shows thatthe speed with which the readjustment of the setting device for changingthe value to be maintained by the regulator is smallest at the beginningof the adjustment and during the time when the amplitude of theregulating oscillation (FIG. 3b) is greatest. The speed is greatest atthe point of inflection of the curve K, whereafter the adjustmentapproaches the new value S at gradually decreasing speed.

With the method according to the invention the total time T needed forthe adjustment is greater than the oscillation period T (FIG. 3b) of thecontrol circuit.

The retardingcharacteristic of the sender must be so adjusted relativelyto the regulating oscillation characteristic of the regulating circuitthat the rule T T is followed for the smallest load change as well asfor the greatest load change of the system.

The dash-dot lines in FIGS. 3a, 3b, and 3c refer to maximal load changesAM and the solid lines to minimal load changes AM. To comply with aminimal load change the value F is increased to F and the value S ischanged to 3' As seen in FIG. 3c the time T for minimal load changes isgreater than the time T' periments have shown that these conditions areobtained with the retarding device according to the invention. If thisdevice is once adjusted so that it agrees with the duration of thecontrol operation in the circuit in which it is used, it operatessatisfactorily at relatively great as well as at relatively smallregulating amplitudes.

FIG. 1 illustrates the application of the invention to a steam powerplant. Feed water is pumped into a steam generator 1 by means of a feedpump 22 through a feed water regulator 8. The feed water passes throughan economizer 23 and therefrom through an evaporating tube system 24 atthe outlet of which a thermostat 2 is arranged for controlling the feedwater supply. The efiluent of the tube system 24 is conducted through awater separator 18 and therefrom through a superheater 25. At the outletof the latter a temperature sensitive device 3, for example, athermostat and a pressure sensitive device 4 are arranged. For producingthe desired steam temperature at the outlet of the superheater 25 a pipe25 is arranged for injecting water into the superheater, the amount ofwater injected being controlled by a regulator 12 which is responsive tothe thermostat 3. Numeral designates a device for controlling the amountof fuel supplied to the steam generator, the amount of combustion airsupplied to the steam generator being controlled by a device 9. Thedevices 9 and 10 are actuated by ,a regulator 11 which is controlledaccording to the pressure in the steam main which acts on a pressuresensitive device 4'.

The steam main 6 connecting the outlet of the superheater 25 with asteam turbine 19 is provided with a steam pressure regulating apparatusincluding a pressure maintaining valve 13 interposed in the steam mainand a relieve valve 14 interposed in a relieve or by-pass pipe 14. Aload measuring apparatus 5 is also connected with the steam main and aturbine inlet valve 15 is interposed in the steam main, the valve 15being responsive to a speed governor 7. The turbine 19 drives anelectric generator 26. The operating medium discharged by the turbine iscondensed in a condenser 20, the condensate being collected in a tank 21from which it is returned to the steam generator by the feed pump 22.

The load measuring device 5 is directly or indirectly operativelyconnected with a sender 16 according to the invention for actuating anapparatus for adjusting the setting of the values to be maintained bythe individual regulators. The pulse emitted by the load measuring andpulse producing device 5 is modified in the sender 16 and transmitted toan apparatus 17 distributing the modified pulses to the individualregulators for adjusting the setting of the values to be maintained bythe individual regulators. The device 17 is illustrated in FIG. 5 andwill be described later. Because of the provision of the load measuringdevice and the sender 16 the in dividual items for operating the steamgenerator as, for example,.the combustion regulator 11, the pressuremain taining apparatus 13, 14, or the temperature regulation which iseffected by the injection regulator 12., 25' and the feed waterregulator 8, are controlled not only in dependence on the steam pressurebut also in dependence on the greatness of the load M, i.e., theregulators must respond to two superimposed control pulses.

Let us assume first that the plant shown in FIG. 1 is in normaloperation and operates at 100% load.

The load measuring device and pulse generator 5 indicates full load andthe modifying device 16 is in its extreme position. The settings of thedistributing device 17 and of adjusting devices connected withregulators 100, 101, 102 and 103 for actuating the feed valve 8, thepressure maintaining valves 13 and t4, the water injection valve 12, andthe heating control device 11, re spectively, are at their end positionscorresponding to load and the regulators for the combustion 11, the feedwater supply 8, etc., maintain an energy condition in the steamgenerating system corresponding to 100% load.

It is now assumed that the load demanded by the consumer 26 is reducedby 50%. In this case, the speed governor 7 closes the inlet valve 15 tomaintain a constant speed of the turbine shaft. This causes an immediateincrease of the pressure in the pressure sensitive devices 4 and 4'. Thepressure sensitive device 4' causes a reduction of the fuel and airsupply by way of the regulator 11 while the pressure sensitive device tprevents an excessive increase of the pressure in the steam main bytemporarily opening the relieve valve 14. The load measuring device 5indicates 50% load and sets the sender 16 to correspond to this load andthe sender begins to transmit the control pulse with retardation toapparatus 17 and therefrom to the devices 100, 101, 102 and 103 forchanging the setting of the values to be maintained by the individualregulators.

Changes of the pressure and of the amounts of operating media flowingthrough the system make themselves felt at the temperature sensitivedevices. The thermostat 3 prevents an excessive temperature increase inthe superheater by opening the water injection regulator 12 and thethermostat 2 increases the feed water supply upon an increase of thetemperature of the operating medium leaving the evaporator 24. Duringthe control period in which a new output condition is produced thevalues to be maintained by the individual regulators are also changed sothat these values correspond to the new load.

The new condition is, therefore, not only obtained by controlling theindividual regulating circuits according to the disturbing pulse causedby the change of load, but also by a new setting of the valuesmaintained by the individual regulators which values now correspond to50% load.

If, after a stable period at 50% load the load is suddenly increased to100%, the control operation is performed as at the previously describedload reduction but in the opposite sense.

FIG. 4 is a more substantial illustration of the regulation of a steampower plant. The operating medium in liquid form is supplied to thesteam generator 1 by means of a feed pump 22 which is connected by meansof a feed pipe 104 with the inlet 105 of a tube system 23, 24 in whichthe liquid is evaporated, the vapor being superheated in a superheater25. The superheated steam emerging from the outlet 106 of thesuperheater 25, is conducted through a steam main 6 to steam consumers.The feed pump 22 is driven by an electric motor 36 receiving powerthrough conduits 37. The speed of the motor 36 is controlled by means ofa regulator 3s. The regulator 38 is actuated by a conventional hydraulicservomotor 39. Operating fluid is supplied to the servomotor 39 througha pipe 4%, the supply of fluid through this pipe being controlled by adevice 41 receiving operating fluid from a temperature sensitive device43 which is connected to and actuated according to the temperature ofthe medium at the connection of the tube system 23, 24 of the steamgenerator with the superheating tube system 25 of the steam generator.The servomotor 39 is not only actuated by fluid coming from or escapingthrough the conduit 40', but also by fiuid which is supplied orwithdrawn through a conduit 44 which is controlled by the device 17 foradjusting the setting of the value to be maintained by the regulator 38.

An injection pump 45 pumps liquid operating medium through a conduit 46into a part of the tube system 23, 24 which is downstream of the pointwhich is connected with the temperature controlled device 43. Theinjection pump 45 is driven by an electric motor 47 which receivescurrent from a supply system through conduits 48. The speed of the motor47 is controlled by a regulator 49 which is actuated by a servomotor 50.The latter is controlled by a device 51 which responds to thetemperature of the steam leaving the superheater 25 and also by theapparatus 17 to which the servomotor G is connected by a conduit 44a andwhich adjusts the setting of the value to be maintained by the regulator49.

A combustion device 52 which receives fuel through a conduit 53 andcombustion air through a conduit 54 is actuated by a servomotor 55 whichresponds to a pressure sensitive device 56 to which it is connected by aconduit 89 and to the apparatus 17 with which it is connected by theconduit 74. Actuation of the combustion control is effected by moving afuel valve spindle 57 and an air damper 58 which are linked to thepiston of the servomotor 55.

The steam in the steam main 6 is conducted either through a pressuremaintaining valve 60 to the inlet valve 15 of a steam engine 19 orthrough a relieve valve 59 and a by-pass conduit, if desired, into acondenser, not shown. The pressure regulating valve 60 is actuated by aservomotor or motor-operator 61. The relieve or bypass valve 59 isactuated by a servomotor or motoroperator 62. The servomotors ormotor-operators 61 and 62 are connected by conduits 64 and 63,respectively, with the device 17 for adjusting the set points of themotor-operators and thereby the reference input of the valves accordingto the load. The servomotor 62 responds also to the pressure sensitivedevice or element 56 to which it is connected by a pulse conduit 80 foropening the valve 59 at excessive pressures in the steam main 6. Theservomotor 61 is connected with the temperature sensitive device orelement 51 by a conduit 89 for closing the valve 60 at an undesiredtemperature reduction in the steam main 6. The reference inputs of thevalves 59 and 60 are so adjusted by the device 17 that the valve 59 isfully closed and the valve 60 is fully open during normal full loadoperation of the plant.

The steam passing through the valve 60 is conducted through the loadmeasuring device 5 before it passes through the inlet valve 15 into theturbine 19. The inlet valve 15 is actuated by a speed governor 7 in theconventional manner. The pulses generated by the load measuring device 5are modified in the pulse modifying device 16 and transmitted to thedevice 17 by a pulse conduit 66.

FIG. 5 shows the apparatus 17 for distributing the modified pulsesreceived from the device 16 according to a predetermined key to theindividual regulators 101, 102, 109 and 103 in FIG. 1 or to theregulators 55, 62, 61, 39 and 50 in FIG. 4 for changing the setting ofthe value to be maintained by the regulators.

The device 17 includes a shaft 67 carrying cams 68 to 71 which are soformed as to produce the desired reference inputs by the regulatorswhich are individually associated with the cams. The shaft 67 can berotated by manipulation of a lever 72. The latter may be connected bysuitable conventional means 66, not shown in detail, with the sender 16for automatic actuation by the latter so that each load measured by thedevice 5 produces a predetermined setting of the reference inputs of theindividual regulators. Each of the cams 68 to .71 actuates a controlpiston 73 which are all alike. The chambers in which the pistons 73 arereciprocally movable are individually connected with the servomotors 39,50, 61, 62, and 55 by conduits 44, 44a, 64, 63, and 74, respectively. Apipe 75 supplies an operating fluid at constant pressure to theapparatus 17. This fluid is distributed into the conduits 44, 64, 63,and 74 at pressures depending on the pressures of springs 76. The lattersit individually in axially movable cups which rest individually on thecams 68 to 71. The ends of the springs protruding from the cupsindividually abut against the control pistons 73. The pressures producedby the springs 76 depend on the angular position of the cams 68 to 71.

The pressure sensitive device 56 comprises a tubular coil spring 77 theinterior of which is connected with the steam main 6. The free end ofthe spring 77 is connected with a slide valve 78 whose position ischanged according to the changes of the steam pressure in the pipe 6.The valve 78 controls the flow of a constant pressure fluid from asupply conduit 79 into a pulse conduit 80 in which the pressure of thefluid corresponds to the position of the valve 78, i.e., to the pressurein the conduit 6.

The servomotor 62 includes a slide valve 84 controlling the flow of aconstant pressure operating fluid from an inlet pipe 82 to an outletpipe 83 and to the sides of a piston 81. The position of the slide valve84 is controlled by the pulse pressures in the conduits 80 and 63 whichact on one end of the valve 84 against the pressure of a spring providedat the other end of the valve. The pulses coming from the conduit 80 areproduced by the pressure sensitive device 56 and tend to actuate thevalve 84 so that the piston 81 which is connected with the relieve valve59 causes opening of the latter when the pres- I sure in the pipe 6exceeds the normal operating pressure. The moment at which the valve 59is actually opened by the piston 81 depends on the position of the cam69 which depends, in a retarded manner, on the amount of steam measuredby the device 5. The mechanism is preferably so set that the relievevalve 59 is opened when the pressure maintaining valve 60 is almostclosed at which time very little or no steam flow is measured by thedevice 5.

The servomotor 61 for the valve 60 includes two piston valves 86 and 90arranged in series with respect to the flow of a constant pressure fluidwhich enters the device 61 at and whose flow to the sides of a workingpiston 87 and to an outlet 88 is controlled by the valves 86 and 90. Thevalve 86 is controlled by the pressure of the pulses in the conduit 64which pressure depends on the angular position of the cam 70 in thedevice 17, the pulse pressures acting on one end of the valve 86 againstthe pressure of a spring provided at the other end of the valve. Thevalve is controlled by the pulse pressure in the conduit 89 which isproduced by the device 51 (FIG. 4) which reacts to the steam temperatureat the outlet of the steam generator 1. The piston 87 is mechanicallyconnected with the valve 60 and, because of the valve 86, actuates thevalve 60 to maintain the steam pressure in the steam main 6 at everyload condition at a value at which the turbine 19 operates at optimumefficiency at that load. Because of the valve 90 the piston 87 actuatesthe valve 60 so that, if the temperature of the steam at the outlet ofthe superheater 25 is too low, the valve 60 is closed to avoid passageof water through the pipe 6 into the turbine 19.

The sender or retarding device transmitting control pulses from the loadmeasuring device 5 is substantially like the one shown in FIG. 2. Therod 28 is not directly connected with the conventional device 5 whosepiston 91 is moved according to the pressures in conduits 92 and 93which are connected with the steam main 6 downstream and upstream of aconventional orifice interposed in the steam main, an auxiliary piston94 being connected with the piston 91 for controlling flow of anoperating fluid to and from a cylinder 95 and moving a piston 96 in thecylinder 95 in synchronism with the movements of the pistons 91 and 94.The rod 28 is connected with the piston 96.

The servomotors 39 and 50 of FIG. 4 are similarly constructed as theservomotors 61 and 62.

I claim:

1. In a steam generating plant comprising a steam generator having atube system for evaporating water antigens and superheating theevaporated water, a live steam conduit connected to the outlet of saidtube system, a device connected to the inlet of said tube system forcontrolling the feedwater supply thereto, and a device for supplyingfuel and air for combustion to the steam generator; a control systemincluding a pressure responsive control pulse generator connected tosaid live steam conduit and producing control pulses corresponding tothe pressureof the live steam produced by the steam generator, atemperature responsive control pulse generator connected to said tubesystem and producing control pulses corresponding to the temperature ofthe produced steam, regulators individually connected to said devicesfor controlling the operation thereof and individually connected. tosaid pulse generators for receiving control pulses therefrom to beactuated thereby for increasing the water supply to said tube systemupon an increase of the temperature of the steam in said tube system andfor increasing the fuel and air supply upon a decrease of the live steampressure, and vice versa, said regulators individually includingadjusting means for changing the control pulses received from said pulsegenerators and thereby altering the effect of the control pulses on saidregulators, a steam flow responsive control pulse producing meansconnected to said live steam conduit and producing pulses correspondingto the amount of live steam flowing through said conduit, and a pulsedelaying means connected to said steam flow responsive control pulseproducing means for delaying the control pulses produced by said steamflow responsive control pulse producing means relatively to the controlpulses produced by said pulse generators, said pulse delaying meansbeing connected to all of said adjusting means for transmitting thedelayed pulses to said adjusting means for actuating the latter afterelapse of a period of time after the pulses produced by said pulsegenerators have actuated the respective regulators for increasing thepressure and temperature affecting said regulators after an increase ofsteam flow and vice versa.

2. In a steam generating plant as defined in claim 1 a pipe branchingoil": from said live steam conduit upstream of the connection of saidpressure responsive pulse generator, a valve in said pipe, a pressureresponsive element connected to said live steam conduit upstream of theconnection of said branch pipe and said live steam conduit for producingcontrol pulses corresponding to the live steam pressure, and a motoroperator operatively connected to said valve and to said element to opensaid valve when the live steam pressure upstream of the valve exceeds apredetermined set point and to close said valve upon decrease of thepressure below the set point, said motor operator including set pointadjusting means operatively connected to said pulse delaying means forchanging the set point of said motor operator after elapse of a periodof time after a change of the steam flow for increasing said set pointafter an increase of steam flow and vice versa.

3. In a steam generating plant as defined in claim 1 a pipe branchingoff from said steam conduit down stream of the connection of saidpressure responsive pulse generator, a valve in said pipe correspondingto the live steam, a motor operator operatively connected to said valveand to said pressure responsive pulse generator to open said valve whenthe live steam pressure exceeds a predetermined set point and to closesaid valve upon decrease of the pressure below the set point, said motoroperator including adjusting means for adjusting the set point, saidadjusting means being operatively connected to said pulse delaying meansfor increasing the set point of said motor operator after elapse of aperiod of time after the steam flow has increased and vice versa, avalve in said live steam conduit downstream of the connection of saidbranch pipe, a second motor operator operatively connected to said valvein said live steam conduit, and a temperature responsive elementconnected to said live steam conduit upstream of said branch pipe andproducing control pulses corresponding to the live steam temperature,said temperature responsive element being operatively connected to saidsecond motor operator to open said valve in said steam conduit uponincrease of the live steam temperature above a predetermined set pointand to close said valve in said conduit upon decrease of the live steamtemperature below the set point, said second motor operator includingadjusting means for adjusting the set point, said adjusting means beingoperative'ly connected to said pulse delaying means for increasing theset point of said second motor operator after elapse of a period of timeafter the steam flow has increased, and vice versa.

4. In a steam generating plant according to claim 1 a temperatureresponsive element connected to said live steam conduit and producingcontrol pulses corresponding to the temperature of the live steam, avalve interposed in said live steam conduit, and a motor operatoroperatively connected" to said valve and to said temperature responsiveelement for actuation of said motor operator in response to the controlpulses produced by said element to close said valve upon decrease of thelive steam temperature below a predetermined temperature, and viceversa, said motor operator including adjusting means for changing thecontrol pulses in response to which said motor operator is actuated,said adjusting means being operatively connected to said pulse delayingmeans for changing the control pulses in response to which said motoroperator is actuated after elapse of a period of time after a change ofthe steam flow for reducing the temperature upon which said valve isclosed, after the steam flow has decreased, and vice versa.

5. The method of controlling the operation of a forced flow steamgenerator at variable rates of steam flow from the generator comprisingthe steps of increasing the rate of heat supply to the steam generatorin immediate response to a decrease of the pressure of the producedsteam below a predetermined pressure forming the set point of the rateof heat supply control, of decreasing the rate of heat supply inimmediate response to an increase of the pressure of the produced steamabove a predetermined pressure, of increasing the rate of feedwatersupply to the generator in immediate response to an increase of thesteam temperature above a predetermined temperature forming the setpoint of the rate of feedwater supply control, of decreasing the rate offeedwater supply to the generator in immediate response to a decrease ofthe steam temperature below a predetermined temperature, and ofdelayedly increasing said predetermined pressure and temperature whichform the set points of the control of the rates of heat and feedwatersupply, upon an increase of the rate of steam flow from the generatorand after effecting said increase of the rate of heat supply and saiddecrease of the rate of feedwater supply, and of delayedly decreasingsaid predetermined pressure and temperature upon a decrease of the rateof steam flow and after effecting said decrease of the rate of heatsupply and said increase of the rate of feedwater supply.

6. The method according to claim 5 wherein completion of the steps ofincreasing or decreasing said predetermined pressure and temperature isdelayed until the regulating oscillations caused by said increase of therate of heat supply and said decrease of the rate of feedwater supply orcaused by said decrease of the rate of heat supply and said increase ofthe rate of feedwater supply have subsided.

7. In a steam power plant comprising a forced flow steam generatorhaving a tube system, means for passing an operating medium through saidtube system, the medium entering the tube system in liquid state andleaving the tube system as superheated steam, and a steam consumerconnected to said generator for receiving steam therefrom, thecombination of means for controlling the 11 rate of heat supply to saidgenerator, means responsive to the pressure of the produced steam andconnected to said heat supply control means for increasing the rate ofheat supply upon a decrease of the pressure of the produced steam belowa predetermined pressure, forming the set point of said rate of heatsupply control means,

of feedwater supply upon a decrease of the temperature of the operatingmedium below a predetermined temperature, forming the set point of saidfeedwater supply control means, and for increasing the rate of feedwatersupply upon an increase of the temperature of the op erating medium,means responsive to the rate of steam flow from said generator to saidconsumer and connected to said means for controlling the rate of heatsupply and of feedwater supply to said generator for increasing thepredetermined pressure and temperature forming the set points of saidcontrol means, upon an increase of the rate of steam flow and fordecreasing the predetermined pressure and temperature of said controlmeans, upon a decrease of the rate of steam flow, and delaying meansinterposed between said rate of steam flow responsive means and saidcontrol means for delaying increase and decrease of said predeterminedpressure and temperature until after said control means have effected achange of the rates of heat and of feedwater supply.

References Cited in the file of this patent UNITED STATES PATENTS1,674,456 Smoot June 19, 1928 2,243,944 Donaldson June 3, 1941 2,470,099Hall May 17, 1949 2,658,516 Luppold et al Nov. 10, 1953 2,664,245OConnor et a1. Dec. 29, 1953 2,804,851 Smoot Sept. 3, 1957

